Ozone generation



Oct. 28, 1952 c. E. THORP EI'AL 2,615,841

OZONE GENERATION Filed July s, 1948 4 heet l EFFECTIVE AREA INVENTORSClark 5 7770279 BYGz/szof P422747 0 ATTO R N EYS Oct. 28, 1952 FiledJuly 8, 1948 C. E. THORP ET AL OZONE GENERATION 4 Sheets-Sheet 2INVENTORS Clark Tharp YGusLzzf Prmula B ATTO RN EYS Oct. 28, 1952 c. E.THORP ETAL 2,515,841

OZONE GENERATION Filed July 1948 4 SheetsSheet 4 INVENTORS Clark .577207 Gustaf Peflu a ATTORNEYS Patented Oct. 28, 1952 UNITED STATESPATENT OFFICE V ozoNE GENERATION Clark E. Thorp, Chicago, and GustafPanu'la,

Mid-lothian, Ill., assignors, by mesne assignments', to Air ReductionCompany, Incorpo-- rated, New York, N. Y., a corporation of New YorkApplication July 8,, 1948,. Serial No. 37,730

pulsating or-alternatin current'i employed, only: a small "portion ofeach pulse or cycle-need be utilized, and that the efficiency isrelated'to the waveform of the energizing potential. Thus 'aconsiderable saving in "power may be effected without decreasing thequantity of ozone generated. ,In accordance with the present inventionit has been discovered that the nature of the voltage (E) which is thepeak vo-ltagebetween electrodes, has'an important relation to efiiciencyin ozone generation.

'In the electrical sense, an ozone generator or purposes of calculationsuch treatment is permissible, although actually the condenser does notpas-s current directly, but allows it to' pass only by storage andsubsequent discharge, as is well known. If direct current is applied asthe" source of potential (E) in constantly increasing magnitude-to anozonizer designed to operate'at', say, 10,000 volts R. M. S., nodischarge will occur at 10,000 volts or at the peak voltage, which isequivalent to approximately 14,250 volts. In fact, experimentshave shownthat no discharge will take place until dielectric breakdown occurs,which in the mentioned case was 32,000 volts. Under such high potential,dielectric breakdown consists in actual puncture and destruction of thedielectric material rendering it useless. Such performance is typical ofelectrical condensers, via, they will pass alternating-or pulsatingcurrent "but not direct current. Therefore, direct current is notsuitable for ozonizer operation. In connection with the followingdescription of the invention it "may be assumed, for. convenience, thatthe power supply for the energizing current is of theiusual alternating60'cycle commercial type.

The operation of the ozonizer when energized by alternating pulses orcurrent may be described 7 Claims; .(Cl. 204-176) as, follows: On thefirst half cycle electrons collec't on the surface-of the positivedielectric." On the second half cycle these electrons flow across to theopposite dielectric, and in colliding with gas molecules existing intheintervening gap' liberate additional electrons. This process is repeatedfor several cycles unti1 electron saturation or equilibrium isestablished, after which the electron density is constant. Theseelectrons flow back and'jforthfrom one dielectric surface to the otheras the cycles of energizing potential alternate the polarity of theelectrodes. Under the mentioned conditions a minimum time is re-- quiredwith eachreversal of .polarity'mr the electronsto leave one dielectricsurface and pass to the opposite dielectricv surface; From this it canbe seen that the 'chance'of' achieving collision betweenelectrons andgas molecules is greatly increased'by reversing the polarityperiodically, and it also explains why a minimum time, 'viz. pulseduration, is required. for substantially all of they electrons to passfrom one dielectric to theop posite dielectric. I

The manner in which the invention may be carried out will be understood:by referenceto the following description considered in connection withthe drawingswhereint I Figs. 1a to if, inclusive, represent severaltypes of Waveforms of energizing voltageiillustrating the principle ofthe invention;

Fig; '2 is a circuit diagram of a pulse genera'tin'g circuit;

Fig; .3 is a schematic diagram of; an electromechanicalsquare-wavegenera-tor;

Fig. 4 is a sideelevation-al view, partly in sec tion, of an Qzonizer inaccordance with the invention;

Fig; 5 is a sectional view of th'eozonizertaken along the'line5-5of'Figf4;

' Fig. Gis an isometric view" of one of the electrode plates representedin Figs-. 4 and5; 'f

Fig. Tillustrates in an isometric 'viewjof which; the end is in section,the manner of assemblying and connectingthe plates of the ozoniz'er;

'Fig'. '8 shows means for making electrical connect'ions'to theelectrode plates,gbeing a'sectional "Referring now. to the firstsh'ee'mr d a ing Fig. 1a illustrates a sine wave which, at least whichseparates the metallic electrodes. This i also increases the powerconsumption because the current passing through a capacitance isproportional to the frequency. Therefore, under ordinary conditions,increasing the frequency alone, while it may increase the ozone yield,does not increase the ,efiiciency because the power consumptionincreases in the same or greater ratio.

In accordance with the invention, an increased yield of ozone withoutincrease in current and,

"in fact, usually with decrease in current, is

voltage is usually the mentioned R. M. S. value.

We have discovered that the area of the .wave

between the zero axis (Fig. 1a) and the value of R. M. S. voltagerepresented by the dotted horizontal lines is, generally speaking,non-effective in producing ozone. In Fig. 1b this ineffective area isshaded by horizontal lines. discovered that the generation of ozone isgreater as the rate of change of voltage becomes greater,

and further that there is an optimum dura--v tion of voltage pulse inrespect to ozone generation efficiency. For example; we have found thata wave or pulse of steep front is more effective than one having a smallrate of change, and that'o'nly a small portion of the voltage Wave iseffective in generating ozone. In other words,

' for the most efi'lcient operation, the voltage wave should have aduration of between 10 and 200 microseconds, and preferably between 100and 200microseconds, per 0.3 cm. of air gap between electrodes. Asan'optimum, a pulse duration of.

approximately 120 microseconds has been calculated, and substantiated bypractice, to produce thelmost ozone per watt of power consumed, moreespecially at approximately 4,000 volts per centimeterof air spacebetween electrodes.

The portion of the voltage wave most effective in generating ozone isrepresented in Fig. lb by the area or sector'sectioned in lines atsubstantially 45 to the horizontal. The correspond: ing' portion of thenegative half-cycle is equally efiective, although it is notspecifically illustrated. Dueto the capacitance effect of the ozonizerdielectric, higher resonant frequencies are usually generated and thesehigh-frequency modulation waves are superimposed on the. peak portionsof the wave as illustrated in Fig. 1b.

It has been stated above that ozone production increases with anincrease of rate of change of voltage, especially with rising voltage.Hence it follows that a wave or pulse of square form viz.,-havingstraight sides perpendicular to the zero axis, rather than of sinusoidalform having curved sloping sides, should, be more effective.

This, in fact, has been demonstrated to be'true, and consequently afirst approach 'to the ideal waveform comprises a square shaped pulse,viz., a straight sided pulse as shown in F g. 1c, of which,

as before, the effective area comprises that portion of the pulseabove'the R M. S. voltagevalue, both plus and minus, of .optimumduration.

Thus, further approaching the ideaLall of the area within the squarewave (Fig. 10) to the right.

of the vertical dotted line between maximum voltage and zero mightbe'eliminated, with considerable saving in electric power, without decreasing the ozone generation. This improvement will result from use ofthe voltage pulses of short duration illustrated in Fig. 1d,whichrepresents a series of voltage pulses of rectangular form, of

optimum duration, spaced apart in regard to the time axis, and ofalternating polarity. The pulse duration can be shortened by increasingthe frequency of the electric power source but this 7 We have alsoachieved by generating voltage of the desired form and duration of waveor pulse and, by employing it to energize an ozonizer, preferably ofimproved construction also according to the invention.

Pulses of short duration which may be employed to produce a greateryield of ozone in the manner of the invention may be obtained in severaldifierent ways. A very simple means comprises the use of a pulsing orsaturating core transformer, which is a device well known in theelectrical art. Pulsing transformers are designed; so that the magneticfiux is increased to satura-- tion in, say, each first quarter cycle ofeach-reversal of the sine wave. Such saturation causes the output of thetransformer to decrease rapidly when the peak voltage is reached,producing .21.. waveform similar to that shown in Fig.'1e. If thepulsing transformer is designed for the in-. tended installation, aneffective voltage peak of comparatively short duration will result, withconsequent-yield of more ozone per watt of energy. than would be thecase if the ozonizer were ener gizedby a sinewave such as illustrated inFig.

lb. As a practical matter it. has been found that the resulting order ofmagnitude of improvement may be expected to be by a factor of more than7.

A more nearly ideal pulse for the present purpose may be obtainedelectronically by an oscillater of the nature shown in Fig.-2,;forexample. Inthis system the initial source of potential is.

high-voltage direct current of say 12,000 volts, or more, applied to theterminals [0, l0, through resistor l I, to a bank ofcondensers 12 whereit is accumulated until a sufiiciently high potential. is

built. up. A gas-discharge .tube [3 of suitable.

high voltage type is connected in the circuit with its anode I4connected to the positive side of the condenser bank. The cathode l5 oftube l3 is in turn. connected to one terminal of the ozonizer l6, theother terminal of the ozonizer being'con-I nected to the negativeterminal of the condenser:

bank I 2. Since grid ll of the tube 13 is connected throu'gh a variablecontact I8 to the grid resistor. |9a, any desired potential may beimpressed on grid I! because the terminals of resisters 1.9, I9a, are,as shown, connected across the condenser banklZ, When tube 13 fires,the.

high voltage from condenser bank I2 will beappliedacross the electrodesof ozonizer l6. Repetition, pulse rate and alternate inversionoffpolarity may be adjusted by selection ofappropriate values of the.components in the timeconstant' networks which include condensers 20 and2 I, inductance23 and resistors I9, l9a. The pulses generated by thesystem of Fig. .2 are illustrated.

in Fig. If, and are seen to'conform quite closelyto the idealwaveformillustrated in Fig. 1d. Pulses ofjthis nature when'applied to asuitable 026- shown in Fig. lb.

ii ltiwill' be noted that the duration of the pulse.

maximum potential which is set by the dielectricstrehgth of thedielectric-material in the ozonizer. By -i-ncrea'singthe pulseduration'to about 100 microsecondsthe sameyield could beobtained at'-about 12,000 volts. r I

I To permit the construction of a pulse generatln'g sys'tem inaccordance with Fig. 2, the followin'g 'values orcircuitelements aregiven entirely byway of example and not by Way of limitation,

it being understood-that those skilled in thehartwouldbe expected tovary the values thereof and modify the connections to suit therequirements in pa'r'ticular cases.

Condensers I2; 0.75 mfd.

Condenser 20 .001 mid.

Condenser 2| ll mid.

Condenser 22 .01 mm.

Resistor l'! 1 megohm Resistor) 1O megohms Resistor 1.9a 0.5 megohmInductance"23 10 millihenries raters Type 4035 (Hydrogen H Thyratron) Ex-perimental results haveindicated that the ozone yield under theassumed conditions is greater with a pulse duration somewhat more than100 microseconds, although, as above stated, the maximum yieldwithminimum power consumption appears to be achieved with a pulse durationof approximately 120 microseconds underthose conditions. Tests show thatasva'riation of about 5 microseconds above or below-120 does"no'tchange' the yield appreciably. For exanipll'e, anincre'ase of ozoneyield by a factor of l8i-' 7"o'ver"that of a'standard ozonizer energizedby-a sine wave was obtained with a pulse durat'i of'125 microseconds.

A practical' and simple means 'for developing pulses of'between aboutl00 and 200 microseconds (which is the preferable range for ozonizers ofthe nature below described) is shown in Fig 3. to consist essentially ofa rotary switch which interrupts a suitable direct-current potential.This rotary switch may be constructed in any suitable manner, and oneexample is illustrated in the drawing. 'In this device, rotor 24,oi'suitable high-voltage insulating material, is supported on and'isdriven by a shaft 25. Therotor carries two brushes, '26 and 21, each ofwhich sho ld be nected together in four separatexgrouos. The

contacts-of each of these .groupsare intercon-i These contacts 28 arecon-.

nected by connectingbuses a, b, c and d, respec-' tively, and thecontacts are arranged in'repeated sequence: a, b, 0, din the directionin which the rotor turns. Ahigh-voltage direct-current source of, say,15,000 volts is connected to the input terminals 30. A suitable filtercomprising inductance 3| and capacitance 32 are connected... as

shown, to the power source. The values ofthese elements would probablybe changed under other conditions, .but those herespecificallyreferredto;

comprise ani inductance of 5 henries: and 1a :ca-r

' pacitance of 10 microfarads. If thedirect-current source is connectedto the bus bars a and c;

and theozonizer i8 is connected to bus bars I) and d, pulses of.substantially square form and of alternating polarity. 'as illustratedin 'Fig. 1d, may. be generated. The frequency of reversaL-as wellas thepulse duration, 1 will .depend upon, the speed of rotation of the rotor24. In this case-theirequency may beassumed tobe 400 cycles per sec!...duration about microwith-the invention is illustrated in Figs.4-8,Z-in-. Referring to Figs- 4 and 5, the ozonizer elusive. includes ahousing S-Sdorming a "gas-tightx cone t'ainer of rectangular shape. Thebottomg-piece 43 of the housing may conveniently beof suitable metalsuch asraluminum, which may be grounded. Preferably. one wall comprisingthe 'front is formed as a removable'door 34 :which includes :a' panel 35of suitable transparent material such as heavy glass, permittingobservation of-thein-L' terior .of the housing,-and especially ofthe;eleca trode platesduring operation; .Thisdoor-Sll may be removablysecuredto thezremainder of the housing by wing-nut damper-36. Tomake.the

door gas tight a suitable gasket t2 may be 'em' ployed. At opposite endsand opposite sides of, the-housing ,gas inlet pipe 31 and-outletpipe-.33 passthroughthewalls to permit the flow of air into theozonizer-and to conduct the resulting-ozone out of the ozonizer.- Acrossthexinlet' end of l the housing a screen 39 of metal or othersuitablematerial issecured to filter the incomin air. The

chamber' formed on the .lopposit side of screen,

39 is largeenough to accommodate the elements orelectrodesyof. theozonizer, which in their as. sembled form are shown in,=Fig...4 and Fig.5.;

The electrode plates-are "preferablyiorcedto-:

gether under pressure, and. for this purpose a.

heavyinsulatingplate 4%. (Fig. 5) is placed at one 'endzof the stack ofplates, and againstthis insulatingplate the necessary pressure isapplied by means: of a screw and hand wheel 4|. By-employing a screw ofproper length, the desired pressure may be applied to any numberofelectrodejplates in-accordance with the requirements.

molding or other process-and comprisesafiat portion'having thickerreinforcing ribs 45.74511. and 45b, extending across theelement; :Theseribs alsoserve as spacers to provide the correct air gaps between theelectrodes.

smooth side of the backing element the'electrode- 416 is secured. Thismay conveniently comprise metal ,foil which in the drawing isrepresentedto "Along the .tioned at right angles to the fuse clips.

be of greater thickness than would probably be necessary. In a typicalcase this foil was about 60 square inches in area, and the thickness ofthe air gap about 0.3 inch. About seventeen such elementsmake aconvenient unit.

Electrical connections to the plates may conveniently be made in themanner illustrated in Fig. 8. A metal rivet or plug 41 is imbedded inthe backing element 44 with the head thereof protruding slightly so asto make electrical contact with the bottom surface of the electrodeplate 46. end ofthe element until it contacts rivet 41. Under the headof screw 48 a U-shaped metal fuse clip 49 is secured so that theconnection from the plate includes rivet 41, screw 48, clip 49, fuse 50and a second fuse clip 49a (Fig. 7). Electrically connected to fuse clip49a by link 6| is another metal U-shaped spring clip posi- By securing a-connection bar 52 which may be of aluminum, for example, into clips 5|of alternate plates, as shown in Fig. '7, these plates will beheld-together and will be electrically interconnected. If the samearrangement of clips, fuses and connection bar is arranged at theopposite ends of the other set of elements they will-also be supportedand their plates interconnected. If the plates of the other set arepreferably supported=by the low-potential or grounded side of thesystem, and if they are also connected thereto it may not be necessaryto fuse those plates. In'the event that fuses 50a (Fig. 4) and fuseclips5la be omitted,the connections to the electrode plates 46 may bemade in the manner shown in Fig. 8, by a screw running from clip 5la toa rivet suitably connected to the electrode plate. In Fig. 5 theassembled plates are illustrated in place within housing 33,. and fromthis figure it is clear that suitable high-potential connection may bemade to bar 52 and low-potential connection may be made to the metalbottom piece 43, to which rod 52a is here shown to be connected.

An alternate modification of the ozonizer is shown in Figs. 9 and 10.This embodiment is I somewhat similar to that of Figs. 4-8, inclusive,

differing therefrom principally in having watercooled elements. In Figs.9 and some of the details of the construction have been omitted, butsuch omitted components may be assumed to be -similar to thoseillustrated in the preceding figures. In this arrangement the metalelectrode plates 53, which are connected to the high potential side ofthe" circuit, are covered on each side by a layer of insulatingmaterial, viz., they are 'imbeclded in an insulating sheet 54. In thealternative, the plate may be interposed between two insulating sheets.Plates 53 should be as thin 'as practicable and should have a verysmooth, flat, ozone-resisting surface. Watercooled electrode plates 55are spaced between the high-potential electrode plates 53. Thesewater-cooled plates are supported by blocks of insulating material 56and 5'! which may suitably be of polystyrene, for example. This materialmay, in fact, be employed for all of the insulating material hereinmentioned, although other insulating materials, such as high-potentialBakelite for example, are also suitable.

The construction of the water-cooled electrode plate is illustrated moreclearly in Fig. 10 which shows it to comprise a hollow metal structureof which the center cavity is filled with water which flows in and outof water pipes 58 and 59.-

A screw 48 is then inserted from the 8. Bailles 60 cause the waterwithin the cavity to circulate more evenly over the entire area. Theseplates are subject to deterioration and should. therefore, be carefullyconstructed. They may be built from'sheet brass heavily cadmium plated.To. form the assembly, water-cooled and noncooled plates can be stackedin alternate layers as illustrated in Fig. 9, and then suitably pressedtogetherby means of the screw and hand wheel 4| as before.

Experienceshows that the question of heating is important in connectionwith ozone generation because the rate ofozone generation is inverselyproportional to the temperature. ozone is more stable at low than athigh tempera tures, the decomposition of the ozone bein n general,proportional to the temperature. Consequently, if the ozonizer or theelectrode plates thereof are not artificially cooled, as by means suchas described in connection with Figs. Sand 10, vpre-cooling of the airpassing intothe ozonizer is desirable. Generally speaking,the;temperature of the air should be low enough to prevent deterioration'of the dielectric and of the electrodes, as well as tov increase theefficiency of ozone generation. I

The air, before being pumped or blown intothe ozonizer, may bepre-cooled by use of a heat exchanger so that the same amount of heatisremoved as will be generated by the ozonizer; "In" this event therelative humidity of the air should be maintained as low as possible,and in any case should not be. permitted to exceed If commonly availableinsulating material is employed in the ozonizer it is advisable tolimit'the rise of temperature of the air such that the temperature doesnot exceed about F. and preferably about half of that value.

In a typical installation employing an ozonizer as described ,inconnection with Figs. 4-8, inclusive, the air from a. power-operatedblower passes through a water-cooled heat exchanger and then into theozonizer inlet pipe 31. The air pressure within the ozonizer mayeffectively be maintained between 700 and 800 millimeters-of mercury,and preferably at about 753 millimeters, or slightly more in theparticular ozonizer herein described. High ozone concentration may behad, by recirculating the output from pipe 38 (Fig. 4)

back into the input as many times asnecessary or by employing aplurality of ozonizers in'serles, or by both expedients. Uponrecirculation; some decomposition of the ozone occurs, butneverthelessrecirculation results in considerably greater.

ozone concentration than is attained by passing the air through'theozonizer but once. 'Within limits, the ozone yield is proportional tothe current density at the electrodes. Current.

density may be increased by increasing. either the frequency, thevoltage or the capacitance in turn, requires the disposal of more heat.'In

some installations this may be a difiicult or'expensive problemdepending, for example, upon the availability and temperature of thesupply Furthermore.

As a practical of cooling water. We have found that a current density offrom about 0.045 to 0.06 milliampere per sq. in. of electrode comprisesa practical range. For optimum efllciency the impedance of thetransformer, or the equivalent, feeding the ozonizer with electric powershould be effectively matched to the load because the power factordecreases with increased current density.

By maintaining an impedance match the power minimum voltage to maximumvoltage and an abrupt decrease from said maximum voltage to said minimumvoltage and a substantially rectangular shape, each of said pulseshaving a predetermined time duration within the range of from 10 to 200microseconds per 0.3 cm. of gas' space between the electrodes.

2. The method of claim 1 in which the time duration of each of thepulses is between 100 and 200 microseconds.

3. The method of claim 1 in which each of the pulses has a time durationof about 120 microseconds and the pulses have a voltage in excess of theionizing voltage of air between the electrodes.

4'. The method of claim 1 in which the voltage pulses are of alternatingpolarity.

5. The method of claim 1 in which heat is V extracted from certain ofthe electrodes so as to maintain the gas in said gap at a temperatureeffectively below the temperature of ozone decomposition.

6. The method of claim 1 in which heat is extracted from the gas withinsaid gap at a rate such as to maintain said gas at a temperatureeffectively below the temperature of ozone decomposition.

7. The method of generating ozone with an ozone generator havingelectrodes separated by a gas space which includes successivelyimpressing on said electrodes while passing oxygen through said gasspace a series of uniformlyspaced, high-potential voltage pulses ofalternating polarity characterized by an abrupt rise from minimumvoltage to maximum voltage and an abrupt decrease from said maximumvoltage to said minimum voltage and a substantially rectangular shape,each of said pulses having a predetermined time duration within therange of from 20 to microseconds per 0.3 cm. of gas space between theelectrodes and less than one-half the time duration of two consecutivepulses of opposite polarity.

CLARK E. THORP. GUSTAF' PANULA.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,162,415 Steynis Nov. 30, 19151,326,631 Bayenk et al. Dec. 30, 1919 1,570,209 De Brey Jan. 19, 19261,793,799 Hartman Feb. 24, 1931 2,072,917 Woelfiin Mar. 9, 19372,127,229 McRae Aug. 16, 1938 2,290,376 Marshall July 21, 1942 FOREIGNPATENTS Number Country Date 369,956 France Dec. 3, 1906 OTHER REFERENCESOzone, Vosmaer, Van Norstrand 00., N. Y.. 1916, pages 64, 68 and 69.

Transactions of the Electro-Chemical Society, vol. 84, 1943, Pp. 83-93.

1. THE METHOD OF GENERATING OZONE WITH AN OZONE GENERATOR HAVINGELECTRODES SEPARATED BY A GAS SPACE WHICH INCLUDES SUCCESSIVELYIMPRESSING ON SAID ELECTRODES WHILE PASSING OXYGEN THROUGH SAID GASSPACE HIGH POTENTIAL VOLTAGE PULSES CHARACTERIZED BY AN ABRUPT RISE FROMMINIMUM VOLTAGE TO MAXIMUM VOLTAGE AND AN ABRUPT DECREASE FROM SAIDMAXIMUM VOLTAGE TO SAID MINIMUM VOLTAGE AND A SUBSTANTIALLY RECTANGULARSHAPE, EACH OF SAID PULSES HAVING A PREDETERMINED TIME DURATION WITHINTHE RANGE OF FROM 10 TO 200 MICROSECONDS PER 0.3 CM. OF GAS SPACEBETWEEN THE ELECTRODES.